Effects of fin pitch on heat transfer and flow resistance of serrated spiral-finned-tube banks

Serrated spiral-finned-tube,developed from solid spiral-finned-tube,has been widely applied in large-scale heat-exchange facility due to its advantages such as easier manufacture,more extended heat transfer surfaces,higher heat transfer coefficient and fin efficiency.For the effects of fin pitch on heat transfer and flow resistance of serrated spiral-finned-tube banks(SSBs),nine SSBs with staggered layouts in terms of various fin pitch were tested based on the analysis on its influencing mechanism.The experimental results are as follows.At the same fin-side Re,Nu increases 19% and Eu decreases 8% with the fin pitch increased from 3.831mm to 4.167mm.The effect of fin pitch on fin-side Nu becomes little when the fin pitch is larger than 4 mm since the gas penetrates the fin-gap more easily and fully flushes the fin-surface.The comprehensive heat transfer performance index j/f(ratio of Colburn heat transfer factor and friction factor)of fin-side first increases and then decreases as Re increases,with higher j/f in Re=7000—10000.At the same fin-side Re,the index j/f is higher as the fin pitch is larger,increased about 28% with the fin pitch increased from 3.831 mm to 4.167 mm.The experimental results were compared with the correlations in literature.The correlations for Nu and Eu on SSBs with staggered layouts, which take fin pitch,transverse pitch and longitudinal pitch of tube banks into accounts,were presented for engineering applications.